1. Field of Invention
The present invention relates to integrated circuits for use in radio receivers. More specifically, the present invention relates to AM converter (amplitude modulated) and AGC (automatic gain control) circuitry suitable for integrated circuit fabrication.
2. Description of Prior Art
To date it has proven inefficient to use integrated circuits (IC's) in lower cost radios. This is due in part to problems involved in moving from discrete components to integrated circuits in tuned multi-function circuits. The tuned circuits cannot yet be made in practical chip form and thus the required number of these elements has not thus far been reduced. I.C. radio tuners today are characterized by large numbers of transistors in the IC and large numbers of connections to the IC chip compared to discrete circuitry. IC's have high tooling costs and high production costs in small volume production. In high volume production runs, on the other hand, the costs are very low. At present, the versatility of IC circuitry has been limited, thus restricting large volume runs of a circuit for low-cost radio tuners.
In short at present low voltage AM radio tuner circuitry suitable for integration in semiconductors has little advantage over discrete circuitry approaches. Present circuitry requires either a large number of components external to the IC, or multiple integrated amplifiers with a large number of connections to the IC, in order to realize the necessary functions of oscillation, mixing, amplifying, automatic gain control and I.F. filtering.